Ecology and Evolution of Photosynthetic Light Responses in the Hawaiian Lobelioids

夏威夷半边莲是植物生态多样化的最壮观的例子之一。这些木本植物出现在高山沼泽，干燥的海崖，潮湿的灌木丛和热带雨林的内部和边缘，并显示出惊人的变化，在生长形式和叶形态。根据PI的DNA家族树，这些植物似乎已经从它们的祖先殖民夏威夷之前和之后不久占据的开阔、阳光充足的地方侵入了密集的阴影栖息地。这个项目的中心目的是了解植物如何获得光合适应阳光与阴凉条件。 PI将试图重建光合生理学，叶片形态，生物化学和整个植物生长的变化时，发生的阴影栖息地从开放的网站入侵。 将研究代表相关夏威夷半边莲类群的物种，包括相对开放的栖息地物种和最近侵入较深阴影的密切相关物种。 将进行实地研究，以确定每个研究物种的自然光环境特征，并测量它们在自然条件下对光的响应。 将进行温室研究，以确定不同的半边莲在光合反应，叶片性状，和整个植物生长在不同的光制度下表现出遗传差异的程度。 此外，这些研究将揭示不同栖息地的物种是否以被认为是有利的方式对光照变化做出反应（例如，在阳光充足的环境中生长的物种是否具有光合速率和叶片特性，从而在明亮的环境中增加生长，而在阴凉处生长相对较差（对于阴影栖息地的物种，反之亦然），以及林下物种--它们栖息在一个不均匀且相对不可预测的光照环境中--显示出比更开放栖息地的物种更有能力改变它们的光合作用形式和生理学以响应变化的光照条件。 结合研究物种之间的进化关系，这些信息将告诉我们在入侵荫凉生境的不同阶段发生了什么变化，哪些特征似乎适应荫凉环境，以及哪些特征似乎受到不同群体进化历史的限制。这项研究将首次让PI调查，在历史框架中，光合作用对阳光与阴影的适应的兴起。这些结果应该增加我们对植物光合性能的生态限制的理解，特别是对半边莲的栖息地要求，其中许多物种已经变得非常罕见。

The Hawaiian lobelioids are one of the most spectacular examples of ecological diversification among plants. These woody plants occur in alpine bogs, dry sea cliffs, moist scrub, and tropical rainforest interiors and edges, and display a striking variety in growth form and leaf morphology. Based on the PIs' DNA family tree for this group, these plants appear to have invaded densely shaded habitats from the open, sunny sites they occupied before and shortly after their ancestors colonized Hawaii. The central aim of this project is to understand how plants acquire photosynthetic adaptations to sunny vs. shady conditions. The PIs will attempt to reconstruct changes in photosynthetic physiology, leaf form, biochemistry, and whole-plant growth that occurred when shady habitats were invaded from open sites. Species representing groups of related Hawaiian lobelioids, including species of relatively open habitats and closely related species that have more recently invaded deeper shade, will be studied. Field studies will be conducted to characterize the natural light environments of each study species and to measure their response in leaf form and photosynthesis to light availability under natural conditions. Greenhouse studies will be conducted to determine the extent to which different lobeliads show genetic differences in photosynthetic response, leaf traits, and whole-plant growth under different light regimes. Furthermore, these studies will reveal whether species of different habitats respond to variation in light in ways thought to be advantageous (e.g., do species of sunny habitats have photosynthetic rates and leaf traits that tend to increase growth in brightly lit environments at the cost of relatively poor growth in the shade (and vice versa for species of shaded habitats), and whether understory species - which inhabit a light environment that is patchy and relatively unpredictable - show more ability to alter their photosynthetic form and physiology in response to changed light conditions than species of more open habitats. When combined with information on the evolutionary relationships among the study species, this information will tell us what changes occurred at different stages in the invasion of shaded habitats, what characteristics appear to be adaptive to shady environments, and what characteristics appear to be constrained by the evolutionary history of the different groups.This research will allow the PIs to investigate, for the first time, the rise of photosynthetic adaptations to sun vs. shade in a historical framework. The results should increase our understanding of the ecological constraints on photosynthetic performance in plants generally, and of the habitat requirements for lobelioids specifically, many species of which have become quite rare.